The present invention relates generally to wireless communication systems and methods, and more specifically to DC offset cancellation for a wireless receiver.
Wireless network technology conveniently allows a mobile user to wirelessly connect to a wired network, such as a local area network (LAN). Heterodyne receivers and direct downconversion receivers are generally used to receive wireless transmissions. In a heterodyne receiver, a radio frequency (RF) signal is mixed with a signal from a local oscillator to produce an intermediate frequency (IF) signal. Through various IF stages with mixers, oscillators, and filters, the IF signal eventually is downconverted to a baseband signal for further processing. Direct downconversion receivers (DCR) directly downconvert a received RF signal to a baseband signal without additional signal processing at various IF stages. The signal is then amplified by a gain to achieve optimal signal strength before presentation to a digital detector or demodulator for further processing.
Both heterodyne receivers and DCRs suffer from same drawbacks. One such drawback is DC offset. DC offset may arise from various sources. Static DC offset (also referred to as coarse DC offsets) may occur due to, for example, temperature, differential input stages, and component mismatches in the components of a receiver. Dynamic DC offset (also referred to as residual DC offset) may occur due to, for example, mixing of the incoming signal with the signal leaked from components of a receiver or signal reflections.
Leakage in components and substantial amplification required to achieve optimal signal strength may result in a large amount of static and dynamic DC offset in a receiver. Without an adequate DC offset correction scheme to remove both static and dynamic DC offset, DC offset may result in loss of information in an incoming signal by generating a large amount of in-band harmonic distortions. Moreover, due to the high data rate often required in a wireless system, DC offsets generally should be quickly removed before interfering with data portions of incoming signals.